We have found that mice suppressed for the Ig-1b allotype have cytotoxic T cells specific for Ig-1b-producing B cells. These so-called Ig-1b Tc cells and two Ig-1b-producing B cells lines (myeloma cells of H-2d and H-2b haplotype) have been adapted to grow continuously in culture; they will be used to examine the fine specificity of interaction between Ig-1b Tc and Ig-1b B cells. In another series of investigations we have defined a new Heavy (H) chain antigen (183-104) on select myeloma and normal Ig's of different classes. Our objective is to determine the H chain location of the 183-104 antigen.